vanilla-lazyload/src/lazyload.autoInitialize.js

A fast, lightweight script to load images as they enter the viewport. SEO friendly, it supports responsive images (both srcset + sizes and picture) and progressive JPEG

/* Creates instance and notifies it through the window element */
const createInstance = function(classObj, options) {
	var event;
	let eventString = "LazyLoad::Initialized";
	let instance = new classObj(options);
	try {
		// Works in modern browsers
		event = new CustomEvent(eventString, { detail: { instance } });
	} catch (err) {
		// Works in Internet Explorer (all versions)
		event = document.createEvent("CustomEvent");
		event.initCustomEvent(eventString, false, false, { instance });
	}
	window.dispatchEvent(event);
};

/* Auto initialization of one or more instances of lazyload, depending on the 
    options passed in (plain object or an array) */
export default function(classObj, options) {
	if (!options) {
		return;
	}
	if (!options.length) {
		// Plain object
		createInstance(classObj, options);
	} else {
		// Array of objects
		for (let i = 0, optionsItem; (optionsItem = options[i]); i += 1) {
			createInstance(classObj, optionsItem);
		}
	}
}